Unstructured databases are becoming a popular alternative to conventional relational databases due to the relaxed format for data storage and the wider range of data structures that may be stored. In contrast to conventional relational databases, where strong typing imposes data constraints to adhere to a predetermined row and column format, unstructured databases impose no such restrictions.
Modern proliferation of data generation for massive quantities of data as well as processing capability to handle large datasets has caused new forms of databases to emerge. These databases differ in many aspects and they are collectively called NoSQL databases (that stands for Not-Only-SQL). What is common in most of these databases is that the data stored within is not confined to a strict structure/schema—hence these databases are sometimes called schema-less or flexible-schema, or unstructured. Some of these documents represent data as a set of documents where each document can have the same structure or different structure as other documents in the collection.
Since such unstructured databases have no formal field or record structure, they may be more accurately characterized as a collection of facts. Unlike their structured counterparts, typically a SQL (Structured Query Language) database, which denotes data in fixed length fields enumerated in records in a tabular form, an unstructured database labels fields for storing values in a document. A set of documents defines a collection, in which the documents in a collection may share some, none, or all of a particular field.